A Serving GateWay (serving GW) is a network node in an Evolved Packet System (EPS) network which tunnels user plane data between a Packet Data Network GateWay (PDN GW) and a base station, i.e. eNodeB (eNB).
If the upper load limit in a serving GW is reached or an operator wants to move a specific subscriber, i.e. user equipment, away from a serving GW, e.g. due to monitoring reasons, then there are no suitable ways to perform that.
Another scenario might be the case when for any reason the operator wants to empty the serving GW from subscribers, i.e. user equipments, in a smooth manor, e.g. at upgrade/update of for instance the serving GW.
A Tracking Area Update (TAU) procedure is performed when a User Equipment (UE) moves outside its Tracking Area (TA) list, i.e. the user equipment detects a change to a new tracking area by discovering that its current TA is not in the list of TAs that the user equipment registered with a Mobility Management Entity (MME). FIG. 1 shows the Tracking Area Update procedure with MME and serving GW change. The steps 108-111 and 117-118 are related to creating, updating and deleting bearer requests, and will be described in detail. The remaining steps will not be described. However a person skilled in the art will understand how they are performed.
Step 108
A target MME sends a create bearer requests to a target serving GW. The target MME determines whether to relocate the serving GW or not. The serving GW is relocated when the source serving GW cannot continue to serve the UE. The target MME may also decide to relocate the serving GW in case a target serving GW is expected to serve the UE longer and/or with a more optimal UE to PDN GW path, or in case a target serving GW and, in some cases, the source serving GW, may be co-located with the PDN GW. If the target MME selected a target serving GW it sends a Create Bearer Request message, comprising e.g. International Mobile Subscriber Identity (IMSI), bearer contexts, to the selected target serving GW. The PDN GW address is indicated in the bearer contexts. The case of selecting one target serving GW is described here, however several target serving GWs may be selected.
Step 109
The target serving GW sends the message Update Bearer Request, comprising e.g. serving GW Address, serving GW Tunnel Endpoint Identifier (TEID), to the PDN GW concerned.
Step 110
The PDN GW updates its bearer contexts and returns an Update Bearer Response message, comprising e.g. PDN GW address and TEID(s), to the target serving GW.
Step 111
The serving GW returns a Create Bearer Response message, comprising e.g. serving GW address and TEID for user plane, serving GW Context ID, to the target MME.
The serving GW updates its bearer context. This allows the serving GW to route Bearer Protocol Data Units (PDUs) to the PDN GW when received from eNodeB.
Step 117
The source MME deletes/frees the EPS bearer resources by sending Delete Bearer Request messages, comprising e.g. TEID, to the source serving GW. The EPS bearer resources may in some cases also be called user equipment bearer resources. It indicates to the source serving GW that the source serving GW shall not initiate a delete procedure towards the PDN GW. If the serving GW has not changed, the serving GW does not delete/free the bearers. If the MME has not changed, step 111 triggers the release of EPS bearer resources, step 117, when a target serving GW is allocated.
As known for a person skilled in the art, an EPS bearer provides PDN connectivity service to a user equipment via EPS access, i.e. it is a “virtual” connection between for example the user equipment and a PDN GW in an Evolved Packet System. An EPS bearer provides a “bearer service”, i.e. a transport service with specific Quality of Service (QoS) parameters. All traffic through an EPS bearer has to use the same set of QoS parameters.
Step 118
The serving GW acknowledges by sending a Delete Bearer Response message, comprising e.g. TEID, to the source MME
The above described tracking area update procedure changes from a source serving GW to a target serving GW, and from a source MME to a target MME when the user equipment changes to a new tracking area.
If the upper load limit in a serving GW is reached or an operator wants to move a specific subscriber, i.e. user equipment, away from a serving GW, then there are no possible ways to perform that.
Another scenario might also be the case when for any reason the operator wants to empty the serving GW from subscribers in a smooth manor, i.e. upgrade/update.
A problem today is that the serving GW node has no means to initiate this move of subscribers which in turn may cause massive rejections during Bearer Setup Procedures, risk of overloading, or causing even worse problems.